Methods of operating a wire bonding machine, including methods of monitoring an accuracy of bond force on a wire bonding machine, and related methods

ABSTRACT

A method of operating a wire bonding machine is provided. The method includes: (a) operating a wire bonding machine during at least one of (i) an automatic wire bonding operation and (ii) a dry cycle wire bonding operation, wherein a bonding force is applied during the operation of the wire bonding machine; and (b) monitoring an accuracy of the bonding force of the wire bonding machine during the at least one of (i) an automatic wire bonding operation and (ii) a dry cycle wire bonding operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.17/517,827 filed Nov. 3, 2021, which claims the benefit of U.S.Provisional Application No. 63/110,012, filed Nov. 5, 2020, the contentsof both of which are incorporated herein by reference.

FIELD

The invention relates to wire bonding operations, and in particular, totechniques for monitoring the accuracy of a bonding force on a wirebonding machine.

BACKGROUND

In the processing and packaging of semiconductor devices, wire bondingcontinues to be the primary method of providing electricalinterconnection between two locations within a package (e.g., between adie pad of a semiconductor die and a lead of a leadframe). Morespecifically, using a wire bonder (also known as a wire bonding machine)wire loops are formed between respective locations to be electricallyinterconnected. The primary methods of forming wire loops are ballbonding and wedge bonding. In forming the bonds between (a) the ends ofthe wire loop and (b) the bond site (e.g., a die pad, a lead, etc.),various types of bonding energy may be used, including, for example,ultrasonic energy, thermosonic energy, thermocompressive energy, amongstothers. Wire bonding machines (e.g., stud bumping machines) are alsoused to form conductive bumps from portions of wire.

Such wire bonding machines typically include a bond head assembly (i.e.,a bond head) that carries a wire bonding tool (e.g., a capillary tool)that contacts a workpiece during the wire bonding operation. Inconnection with most wire bonding operations, a bonding force is appliedto the wire bonding tool. In order to form consistent (and acceptable)wire bonds, it is important that the bonding force applied during wirebonding is accurate. However, sometimes the applied force is differentfrom an intended (e.g., programmed) bonding force. For example, thebonding force may vary over time based on conditions such asenvironmental factors, hours of machine operations, amongst others.

Thus, it would be desirable to provide improved techniques formonitoring and/or controlling the bonding force on a wire bondingmachine.

SUMMARY

According to an exemplary embodiment of the invention, a method ofoperating a wire bonding machine is provided. The method includes: (a)operating a wire bonding machine during at least one of (i) an automaticwire bonding operation and (ii) a dry cycle wire bonding operation,wherein a bonding force is applied during the operation of the wirebonding machine; and (b) monitoring an accuracy of the bonding force ofthe wire bonding machine during the at least one of (i) the automaticwire bonding operation and (ii) the dry cycle wire bonding operation.

According to another exemplary embodiment of the invention, a method ofoperating a wire bonding machine is provided. The method includes thesteps of: incrementally adjusting a bonding force applied to a bond headassembly while detecting a z-height position of a portion of the bondhead assembly; and determining a desired bonding force at which anincremental adjustment does not result in a change of the z-heightposition of the bond head assembly.

According to another exemplary embodiment of the invention, a method ofoperating a wire bonding machine is provided. The method includes thesteps of: incrementally adjusting a bonding force applied to a bond headassembly while detecting a z-height position of a portion of the bondhead assembly; and determining a desired bonding force at which anincremental adjustment from results in a peak z-height position of thebond head assembly.

According to yet another exemplary embodiment of the invention, a methodof operating a wire bonding machine is provided. The method includes thesteps of: incrementally decreasing a bonding force applied to a bondhead assembly while detecting a z-height position of a portion of thebond head assembly, until the z-height position changes from an initialheight by a predetermined height adjustment; and detecting a bondingforce value upon the z-height position changing from the initial heightby the predetermined height adjustment.

According to yet another exemplary embodiment of the invention, a methodof operating a wire bonding machine is provided. The method includes thesteps of: incrementally increasing a bonding force applied to a bondhead assembly while detecting a z-height position of a portion of thebond head assembly, until the z-height position changes from an initialheight by a predetermined height adjustment; and detecting a bondingforce value upon the z-height position changing from the initial heightby the predetermined height adjustment.

The methods of the invention may also be embodied as an apparatus (e.g.,as part of the intelligence of a wire bonding machine), or as computerprogram instructions on a computer readable carrier (e.g., a computerreadable carrier including a wire bonding program used in connectionwith a wire bonding machine).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIGS. 1A-1C are a series of block diagram side views of a wire bondingmachine illustrating a method of operating a wire bonding machine inaccordance with an exemplary embodiment of the invention;

FIGS. 2A-2C are another series of block diagram side views of a wirebonding machine illustrating a method of operating a wire bondingmachine in accordance with an exemplary embodiment of the invention;

FIGS. 3A-3F are yet another series of block diagram side views of a wirebonding machine illustrating a method of operating a wire bondingmachine in accordance with an exemplary embodiment of the invention;

FIG. 4 is a timing diagram illustrating a z-height position of a portionof a bond head assembly, and the bonding force applied by the bond headassembly, versus time, in accordance with an exemplary embodiment of theinvention; and

FIGS. 5-8 are flow diagrams illustrating methods of operating wirebonding machines in accordance with various exemplary embodiments of theinvention.

DETAILED DESCRIPTION

In accordance with various exemplary embodiments of the invention,methods of operating wire bonding machines are provided, for example,methods of automatically verifying bonding force (sometimes referred toas bond force), and methods of monitoring bonding force in real time, ona wire bonding machine. In certain embodiments of the invention, themethods may include an automatic mode bonding force verification processand/or a closed loop bonding force adjustment process (e.g., includingoffset adjustments of the bonding force).

Thus, aspects of the invention relate to the monitoring and/or theautomatic correction/adjustment of bonding force applied on a wirebonding machine, with the goal of achieving a desirable wire bondingperformance. For example, according to aspects of the invention, thebonding force (and/or the accuracy of the bonding force) is monitored inan automatic wire bonding mode (and/or a dry cycle bonding mode), wherea response may be provided if the accuracy of the monitored bondingforce is not within an acceptable range (e.g., the monitored bondingforce has shifted due to any reason). For example, the response may be(i) to provide an alarm, warning or error message to a machine operator;(ii) to cease operation of the wire bonding machine; (iii) toautomatically adjust the bonding force of the wire bonding machine(e.g., closed loop force offset adjustment); etc.

According to certain exemplary embodiments of the invention, methods areprovided for verifying the machine bonding force in automatic mode. Suchmethods may include applying multiple levels of bonding force, andmonitoring the response of the bond head position. For example, thestarting force (e.g., a pre-verified force F_(pv), which may or may notbe a zero gram force) may be gradually decreased in small incrementsuntil it moves up a set height (e.g., h_(a)), and then the force may beincreased until it moves back down to the starting point (e.g.,h_(init)). This force verification can be performed at dry cycle andautomatic mode. The two force values (and/or additional force valuessuch as F_(b) within the scope of the invention) (e.g., the force valuecorresponding to the set height h_(a), and the force value correspondingto the return to the starting point h_(init)) are recorded. If the forcevalues do not meet the expectation (e.g., are not within an acceptabletolerance of the expected force values), a response may be provided(e.g., the response may be: to provide an alarm, warning or errormessage to a machine operator; to cease operation of the wire bondingmachine; to automatically adjust the bonding force of the wire bondingmachine to an acceptable level).

The invention provides significant advantages over past practice.Existing methods of bonding force calibration involve operatorsperforming calibrations offline (not in automatic mode). Suchcalibrations tend to be time consuming, and require the removal ofcertain hardware parts (e.g., a flow head for reducing gas), and theinstallation of calibration weights. Aspects of the invention provideforce verification in automatic mode with a minimal (or no) timepenalty, and may also be used to provide closed loop bonding forceadjustments.

Aspects of the invention relate to monitoring an accuracy of the bondingforce of a wire bonding machine during at least one of (i) an automaticwire bonding operation and (ii) a dry cycle wire bonding operation.Exemplary techniques for monitoring such accuracy of the bonding forceare disclosed herein. However, other techniques for accomplishing suchmonitoring (during at least one of an automatic wire bonding operation,and a dry cycle wire bonding operation) are contemplated within thescope of the invention.

As used herein, the term “zero gram force” is an example of an appliedbonding force at which an incremental force adjustment (e.g., anincrease or decrease in the bonding force) does not result in a changeof the z-height position of the bond head assembly. The term “zero gramforce” may also be used to refer to an applied bonding force thatresults in a peak height (either a high peak height or a low peakheight) of a portion of a bond head assembly (e.g., force F_(b)resulting in height h_(b), and force F_(d) resulting in height h_(d),both described in connection with FIG. 4 ). In any case, such “zero gramforce” values may be determined from a single value (e.g., see F_(b)from FIG. 4 , F_(d) from FIG. 4 , etc.). Further, a determined “zerogram force” or a determined “desired” force within the scope of theinvention may utilize multiple measured values (e.g., see F_(b) fromFIG. 4 , F_(d) from FIG. 4 , etc.) to determine a single force value.For example, a single force value may be determined by averaging (orotherwise mathematically manipulating) the multiple measured values froma single cycle (as in FIG. 4 ) or multiple cycles.

Aspects of the invention relate to detecting a bonding force applied atdifferent height positions of a bond head assembly of a wire bondingmachine. For example, a force value may be detected upon the z-heightposition changing from one height to another height (e.g., changing froman initial height by the predetermined height adjustment). In otheraspects of the invention, height positions of a bond head assembly of awire bonding machine are detected at different values of applied bondingforce. Using such bonding force and/or height position information, theaccuracy of the bonding force may be monitored.

While the invention is largely described in connection with a forcecontrol mode of a wire bonding machine, it is not limited thereto. Forexample, a position control mode may be utilized. In connection withsuch a position control mode, a characteristic of a z-axis driving force(which corresponds to a bonding force) may be determined whilesubstantially maintaining a predetermined z-axis position to monitor theaccuracy of the bonding force. Such a characteristic may be, forexample, an electrical characteristic of a z-axis motor, an electricalcurrent of a z-axis motor providing the driving force, etc.

Throughout the various drawings provided herein, the same referencenumbers refer to the same element. Thus, a description of certainelements may be omitted in connection with some of the drawings.

Referring now to the drawings, FIGS. 1A-1C illustrate wire bondingmachine 100. Wire bonding machine 100 includes support structure 102(e.g., a heat block, an anvil, etc.) for supporting a workpiece 104(e.g., a semiconductor element such as a leadframe holding one or moresemiconductor die) during a wire bonding operation. In FIG. 1A, wirebonding machine 100 also includes wire bonding tool 108 (e.g., acapillary wire bonding tool, a wedge bonding tool, etc.) for bondingwire portions to workpiece 104. As will be appreciated by those skilledin the art, wire bonding tool 108 (carried by bond head assembly 110) ismoveable along a plurality of axes of wire bonding machine 100 toperform wire bonding operations. For example, wire bonding tool 108 maybe moved along the x-axis and y-axis through movement of bond headassembly 110. A linkage 110 a is provided as part of the bond headassembly 110. Linkage 110 a is configured for movement along the z-axisof the wire bonding machine 100 with the bond head assembly 110, and isdriven along the z-axis by z-axis motor 116 (which is controlled bycomputer 114 of wire bonding machine 100). A z-axis position detector112 (e.g., a z-axis encoder) is provided that detects the z-axisposition of linkage 110 a (and hence a relative z-axis position of wirebonding tool 108), and provides data corresponding to this z-axisposition (e.g., real time) to computer 114 of wire bonding machine 100.Thus, computer 114 has information related to the z-axis position ofwire bonding tool 108 through its motions. In a force control mode,z-axis motor 116 may be used to apply bonding force in connection withwire bonding operations.

Referring specifically to FIG. 1A, free air ball 106 is seated at aworking tip 108 a (the contact portion) of wire bonding tool 108. Insome embodiments, free air ball 106 is not required within the scope ofthe invention (e.g., the inventive methods may be performed with no wireportion at working tip 108 a). The initial height shown in FIG. 1A ish_(init) (e.g., see left side of timing diagram in FIG. 4 , describedbelow in connection with FIG. 3A). While h_(init) is shown with respectto the working tip 108 a of wire bonding tool 108 (adjacent free airball 106), this is a relative height, and could be illustrated withrespect to any part of bond head assembly 110 that moves along thez-axis. At this stage, a bonding force applied to the bond head assembly110 (e.g., through z-axis motor 116) is incrementally decreased whiledetecting a z-height position of a portion of the bond head assembly 110(using z-axis position detector 112), until the z-height positionchanges from h_(init) by a predetermined height adjustment (in FIG. 1B,until it reaches height h_(a)) (e.g., see h_(a) in the timing diagram inFIG. 4 , described below in connection with FIG. 3B). During thisincremental decrease in bonding force, the bonding force value isdetected upon the z-height position changing from h_(init) by thepredetermined height adjustment shown in FIG. 1B. Then, the bondingforce applied to the bond head assembly 110 is incrementally increasedwhile detecting the z-height position of the portion of the bond headassembly 110 (using z-axis position detector 112), until the z-heightposition returns to h_(init) as shown in FIG. 1C (e.g., see h_(init) ascaused by F_(c) in the timing diagram in FIG. 4 , described below inconnection with FIG. 3D). During this incremental increase in bondingforce, the bonding force value is detected upon the z-height positionchanging back to h_(init) as shown in FIG. 1C. Using these detectedbonding force values, the accuracy of the bonding force (e.g., includingthe accuracy of the zero gram force) may be monitored (e.g., theaccuracy of the applied bonding force as compared to the intended (e.g.,programmed) bonding force). Of course, variations, and additionalprocess steps, may be included in this exemplary process.

The process illustrated in FIGS. 1A-1C is just one technique formonitoring the accuracy of the bonding force (and/or method of operatinga wire bonding machine). FIGS. 2A-2C illustrate another non-limitingexample. Referring specifically to FIG. 2A, the initial height shown ish_(init). While h_(init) is shown with respect to the working tip 108 aof wire bonding tool 108 (adjacent free air ball 106), this is arelative height, and could be illustrated with respect to any part ofbond head assembly 110 that moves along the z-axis. At this stage, abonding force applied to bond head assembly 110 (e.g., through z-axismotor 116) is incrementally increased while detecting a z-heightposition of a portion of bond head assembly 110 (using z-axis positiondetector 112), until the z-height position changes from h_(init) by apredetermined height adjustment (in FIG. 2B, until it reaches heighth_(a)). During this incremental increase in bonding force, the bondingforce value is detected upon the z-height position changing fromh_(init) by the predetermined height adjustment shown in FIG. 2B. Then,the bonding force applied to bond head assembly 110 is incrementallydecreased while detecting the z-height position of the portion of bondhead assembly 110 (using z-axis position detector 112), until thez-height position returns to h_(init) as shown in FIG. 2C. During thisincremental decrease in bonding force, the bonding force value isdetected upon the z-height position changing back to h_(init) as shownin FIG. 2C. Using these detected bonding force values, the accuracy ofthe bonding force (e.g., including the accuracy of the zero gram force)may be monitored (e.g., the accuracy of the applied bonding force ascompared to the intended (e.g., programmed) bonding force).

FIGS. 3A-3F illustrate another non-limiting example for monitoring theaccuracy of the bonding force (and/or method of operating a wire bondingmachine). FIG. 4 is a timing diagram illustrating a z-height position ofa portion of the bond head assembly, and the bonding force applied bythe bond head assembly, versus time. The timing diagram of FIG. 4 alignswith the process steps shown in FIGS. 3A-3F as described below.

Referring specifically to FIG. 3A, wire bonding machine 100 isillustrated with free air ball 106 at a position h_(init). The forceapplied at this point can be described as the pre-verified zero gramforce (see “F_(pv)” of FIG. 4 ). In FIG. 3B, wire bonding tool 108 ismoved upward (i.e., +Z direction) to position h_(a) as the applied forceto wire bonding tool 108 is decreased (this is illustrated in FIG. 4 asthe applied force changes from F_(pv) and F_(a)) (See FIG. 4 , where aforce F_(a) is applied, at which time the applied force begins toincrease). In FIG. 3C, wire bonding tool 108 continues to move upward toa position h_(b) even though the force is increasing (this isillustrated in FIG. 4 between points h_(a) and h_(b)), for example, dueto the momentum of bond head assembly 110. A zero gram force (e.g.,force F_(b)) may be determined/monitored at this point (i.e., at heighth_(b), where the height is at a local maxima). Thus, in connection withFIG. 3C, a zero gram force may be determined in connection with anapplied bonding force that results in the peak height h_(b) (i.e., forceF_(b) resulting in height h_(b), as described in connection with FIG. 4).

In FIG. 3D, wire bonding tool 108 is moved back to the initial positionh_(init) when the applied force is at its peak, F_(c) (this isillustrated in FIG. 4 between points F_(b) and F_(c)). In FIG. 3E, wirebonding tool 108 is moved to position h_(d) as the applied force isbeing decreased (this is illustrated in FIG. 4 between points F_(c) andF_(d)). Another zero gram force (e.g., F_(d)) may bedetermined/monitored at this point (i.e., h_(d), where the height is ata local minima). That is, in connection with FIG. 3E, a zero gram forcemay be determined in connection with an applied bonding force thatresults in the peak height h_(d) (i.e., force F_(d) resulting in heighth_(d), as described in connection with FIG. 4 ).

In FIG. 3F, wire bonding tool 108 moves back to position h_(init) as theapplied force continues to decrease (this is illustrated in FIG. 4between points F_(d) and F_(e)).

The timing diagram illustrated in FIG. 4 is a short duration (e.g., asingle cycle), however, it is understood that this process shown in FIG.4 (or any part thereof claimed in this application) may be repeated fora plurality of cycles until the desired result occurs (e.g., a desiredbonding force is determined, a stable bonding force value is determined,an accurate zero gram force value is determined, the accuracy of thebonding force has been determined, etc.).

FIGS. 5-8 are flow diagrams illustrating methods of operating wirebonding machines (and related methods) in accordance with variousexemplary embodiments of the invention. As is understood by thoseskilled in the art, certain steps included in the flow diagrams may beomitted; certain additional steps may be added; and the order of thesteps may be altered from the order illustrated.

Referring specifically to FIG. 5 , a method of operating a wire bondingmachine is illustrated. At Step 500, a wire bonding machine is operatedduring at least one of (i) an automatic wire bonding operation and (ii)a dry cycle wire bonding operation, wherein a bonding force is appliedduring the operation of the wire bonding machine. At Step 502, anaccuracy of the bonding force of the wire bonding machine is monitoredduring the at least one of (i) the automatic wire bonding operation and(ii) the dry cycle wire bonding operation. For example, in Step 502, theaccuracy of an applied bonding force as compared to the intended (e.g.,programmed) bonding force may be monitored.

For example, Step 502 may occur during a force control mode (or aposition control mode) of operation of the wire bonding machine. DuringStep 502, a force applied to a bond head assembly of the wire bondingmachine may be incrementally adjusted (e.g., incrementally increasing aforce, incrementally decreasing a force, both incrementally increasingand decreasing a force, etc.) while detecting a z-height position of aportion of the bond head assembly.

Additional aspects of the invention may also occur during Step 502. Forexample, an accurate zero gram force may be determined during Step 502.For example, in connection with Step 502, a desired force may bedetermined at which an incremental adjustment from Step 500 does notresult in a change of the z-height position of the bond head assembly.Stated differently, a desired force may be determined at an appliedforce where an incremental adjustment from Step 500 results in a peakz-height position of the bond head assembly (e.g., force F_(b) resultingin height h_(b), force F_(d) resulting in height h_(a), both asdescribed in connection with FIG. 4 ).

Further, during Step 502, the wire bonding tool may be being positionedabove, and not in contact with, a workpiece on the wire bonding machine.Alternatively, during Step 502, the wire bonding tool may be in contactwith a workpiece on the wire bonding machine.

At optional Step 504, a response is provided if the accuracy of thebonding force monitored during Step 502 is not within an acceptablerange. For example, the response may include at least one of: (a)providing an alarm to a machine operator, (b) providing a warning to themachine operator, (c) providing an error message to the machineoperator, (d) ceasing operation of the wire bonding machine, and (e)automatically adjusting the bonding force of the wire bonding machine.

Referring now to FIG. 6 , another method of operating a wire bondingmachine is illustrated. At Step 600, a bonding force applied to a bondhead assembly is incrementally adjusted (e.g., incrementally increasingthe bonding force, incrementally decreasing the bonding force, bothincrementally increasing and decreasing the bonding force, etc.) whiledetecting a z-height position of a portion of the bond head assembly. AtStep 602, a desired bonding force is determined at which an incrementaladjustment from Step 600 does not result in a change of the z-heightposition of the bond head assembly. For example, the desired bondingforce may be a zero gram force. An alternative to Step 602 would be todetermine the desired force at an applied force where an incrementaladjustment from Step 600 results in a peak z-height position of the bondhead assembly (e.g., force F_(b) resulting in height h_(b), force F_(d)resulting in height h_(d), both as described in connection with FIG. 4).

As will be appreciated by those skilled in the art, Steps 600 and 602may be repeated for a plurality of cycles until the desired bondingforce is determined at a stable value by a wire bonding machine at Step602. Further, Steps 600 and 602 may occur during a force control mode(or a position control mode) of operation of a wire bonding machine.

Referring now to FIG. 7 , yet another method of operating a wire bondingmachine is illustrated. At Step 700, a bonding force applied to a bondhead assembly is incrementally decreased while detecting a z-heightposition of a portion of the bond head assembly, until the z-heightposition changes from an initial height (e.g., h_(init)) by apredetermined height adjustment (e.g., see height adjustment to heighth_(a) in FIG. 1B and FIG. 3B). At Step 702, a bonding force value (e.g.,see F_(a) in FIG. 4 , referring to h_(a) from FIG. 1B or FIG. 3B) isdetected upon the z-height position changing from the initial height bythe predetermined height adjustment. At optional Step 704, after Step702, the bonding force applied to the bond head assembly isincrementally increased while detecting the z-height position of aportion of the bond head assembly, until the z-height position returnsto the initial height (e.g., see return to h_(init) in FIG. 1C and FIG.3D, corresponding to bonding force F_(c) from FIG. 4 ).

After Step 700, the z-height position may continue to change until itreaches a peak height position (e.g., see height h_(b) from FIG. 3C,corresponding to bonding force value F_(b)).

Further, Steps 700 and 702 may occur during a force control mode (or aposition control mode) of operation of a wire bonding machine.

Referring now to FIG. 8 , yet another method of operating a wire bondingmachine is illustrated. At Step 800, a bonding force applied to a bondhead assembly is incrementally increased while detecting a z-heightposition of a portion of the bond head assembly, until the z-heightposition changes from an initial height (e.g., h_(init)) by apredetermined height adjustment (e.g., see height adjustment to heighth_(a) in FIG. 2B). At Step 802, a bonding force value (e.g., the bondingforce corresponding to height h_(a) in FIG. 2B) is detected upon thez-height position changing from the initial height by the predeterminedheight adjustment. At optional Step 804, after Step 802, the bondingforce applied to the bond head assembly is incrementally decreased whiledetecting the z-height position of the portion of the bond headassembly, until the z-height position returns to the initial height(e.g., see return to h_(init) in FIG. 2C). In connection with this Step804, a bonding force value may be detected upon the z-height positionreturning to the initial height.

In connection with the method of FIG. 8 , after Step 800, the z-heightposition may continue to change until it reaches a peak height position.At this peak height position, the bonding force value may be detected.

Further, Steps 800 and 802 may occur during a force control mode (or aposition control mode) of operation of a wire bonding machine.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A method of operating a wire bonding machine, themethod comprising the steps of: (a) incrementally decreasing a bondingforce applied to a bond head assembly while detecting a z-heightposition of a portion of the bond head assembly, until the z-heightposition changes from an initial height by a predetermined heightadjustment; and (b) detecting a bonding force value upon the z-heightposition changing from the initial height by the predetermined heightadjustment.
 2. The method of claim 1 wherein the bonding force value isF_(a).
 3. The method of claim 1 wherein, after step (b), the methodincludes incrementally increasing the bonding force applied to the bondhead assembly while detecting the z-height position of a portion of thebond head assembly, until the z-height position returns to the initialheight.
 4. The method of claim 3 wherein the bonding force value uponthe z-height position returning to the initial height is detected asF_(c).
 5. The method of claim 1 wherein, after step (a) the z-heightposition continues to change until it reaches a peak height position. 6.The method of claim 5 wherein the bonding force value upon the z-heightposition reaching the peak height position is detected as F_(b).
 7. Themethod of claim 1 wherein steps (a) and (b) occur during a force controlmode of operation of a wire bonding machine.
 8. A method of operating awire bonding machine, the method comprising the steps of: (a)incrementally increasing a bonding force applied to a bond head assemblywhile detecting a z-height position of a portion of the bond headassembly, until the z-height position changes from an initial height bya predetermined height adjustment; and (b) detecting a bonding forcevalue upon the z-height position changing from the initial height by thepredetermined height adjustment.
 9. The method of claim 8 wherein, afterstep (b), the method includes incrementally decreasing the bonding forceapplied to the bond head assembly while detecting the z-height positionof the portion of the bond head assembly, until the z-height positionreturns to the initial height.
 10. The method of claim 9 wherein thebonding force value upon the z-height position returning to the initialheight is detected.
 11. The method of claim 8 wherein, after step (a)the z-height position continues to change until it reaches a peak heightposition.
 12. The method of claim 11 wherein the bonding force value isdetected upon the z-height position reaching the peak height position.13. The method of claim 8 wherein steps (a) and (b) occur during a forcecontrol mode of operation of a wire bonding machine.